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Homework Help: Two metal rods, one silver and the other copper, are both immersed at

  1. Jun 25, 2014 #1
    1. The problem statement, all variables and given/known data
    Two metal rods, one silver and the other copper, are both immersed at one end in a steam chamber at a temperature of 100°C. The other end of each one is in an ice water bath at 0°C. The rods are 5.0 cm long and have a square cross-section that is 2.0 cm on a side. No heat is exchanged between the rods and the surroundings, except at the ends. How much total heat flows through the two rods each minute? The thermal conductivity of silver is 417 W/m • K, and that of copper is 395 W/m • K.

    2. Relevant equations
    I think it is H = (k*A*DT)/L

    3. The attempt at a solution
    I plugged each k separately and got 226 and 248 which are none of the answer choices.
  2. jcsd
  3. Jun 25, 2014 #2


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    Staff: Mentor

    No idea what is the correct approach, but I am not surprised what you did doesn't yield a correct answer.

    Assuming two copper rods, how much total heat would you expect?
  4. Jun 25, 2014 #3
    The formula is OK. Check your calculations. Or show them here.
  5. Jun 25, 2014 #4


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    Gold Member

    I don't think this is your only problem but it's "a" problem...

    The formula gives the power in Watts but the question asks..

    .. which would be a figure in joules.

    I say it's not the only problem because I got different values for the power in watts in each rod.
  6. Jun 25, 2014 #5
    The problem asks for the heat that flows in 2 minutes. Once you have the power you can find the energy.
    But the OP did not specify the units for the two values he got so is not clear what quantities they are supposed to represent.
  7. Jun 27, 2014 #6

    rude man

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    Your formula is OK if

    H = heat RATE (not heat), W
    k = thermal conductivity, W/m
    A = area, m^2
    DT = temperature difference = 100C
    L = length of rod, m

    Obviously, the total heat rate is the sum of the heat rate of each bar. Then, heat = heat rate times time. Unit of heat is the Joule in SI units. Joules = watts x seconds.

    Your answers are way, way too low.

    @nasu: the question asks for the total heat conducted over 1 minute, not 2.
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